Listen in: Can a vibration energy harvester replace batteries?

Micro generators promise a supply of free energy to power instrumentation devices. Are they practical?

06/19/2008


With the growth of wireless devices in process plants, the need for self-contained power options also is growing. Batteries are an obvious choice, but small energy scavengers promise to generate free power from ambient sources. Can they save you money?

The answer depends on how often you have to replace batteries and how complicated that process is. If your maintenance people spend a lot of time on dead batteries, you might want to explore these other options. One possibility could be a vibration energy harvester such as those made by Perpetuum . ( Click here to hear energy harvesting comments from Roy Freeland, Perpetuum CEO .)

These devices generate power from vibrations, which can come from motors, compressors, piping, and so forth. Simply stated, more vibration delivers more power. Frequency also has a major influence. The trickiest part of designing for one of these will be figuring out how much you’re going to get in a given application because the output can be over a wide range. For example, output charts say the same unit can provide 1 to 50 mW. If you have appropriate vibration measurements, you can do the calculations, but Freeland’s rule of thumb says you can assume power output roughly equivalent to an AA battery.

If you’re interested in this technology, experimentation will be in order. You’ll probably have to buy one and see where it works best. Since vibration is usually considered a bad thing for equipment, you’ll also need to make sure your maintenance department isn’t trying to quiet down that motor you’re planning on using. One person’s efforts to extend bearing life could starve your energy harvester. Moreover, you need to ensure the thing doing the vibrating doesn’t shut down while you still need power. On the other hand, those involved say it doesn't take much vibration to create power.

You can buy many batteries for the cost of one vibration generator, so the cost trade-off will depend on battery replacement frequency, replacement cost, and potential problems from being without a device during replacement. That’s an evaluation you will have to make for yourself.

—Peter Welander, process industries editor, PWelander@cfemedia.com ,
Process Instrumentation & Sensors Monthly
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